Phonograph turntable assembly



July 31, 1962 F. H. DRAKE 3,047,297

PHONOGRAPH TURNTABLE ASSEMBLY Filed July '7, 1958 4 Sheets-Sheet l FIG.I

FIG.2

ATTORN EY July 31, 1962 F. H. DRAKE 3,047,297

PHONOGRAPH TURNTABLE ASSEMBLY Filed July 7, 1958 4 Sheets-Sheet 2 2FIG.3

INVENTOR. Frederick H. Drake W7M/WM ATTORNEY July 3-1, 1962 F. H. DRAKE3,047,297

PHONOGRAPH TURNTABLE ASSEMBLY Filed July 7, 1958 4 Sheets-Sheet 3 O JINVENTOR.

L l FREDERICK DRAKE ATTORNEYS United States Patent 3,047,297 PHONOGHTURNTABLE ASSENBLY Frederick H. Drake, Boonton, N .J.

(Squire Road, Roxbury, Conn.) Filed July 7, 1958, Ser. No. 747,093 6Claims. (Cl. 274-49) The invention relates to phonograph turntableassemblies and more particularly to supporting structures for isolatingthe record table and pick-up arm from spurious vibrations which wouldimpair sound reproduction from the record. This is acontinuation-in-part application of my co -pending application, SerialNo. 678,818, filed August 19, 1957 now abandoned.

It is the present practice in the best phonograph turntable assembliesto mount the record turntable, the driving motor for the turntable, andthe pick-up arm on the same mounting board or cabinet. Such assembliesemploy a massive table which is usually belt "driven to minimize thetransmission of vibrations from the driving motor to the table andrecord; and to minimize the transmission of motor vibrations to themounting board, mechanical vibration filters are usually interposedbetween the motor and the mounting board. However, in spite of these andother precautions some spurious vibrations from the motor and from othersources are always present in the mounting board of even the bestturntable assemblies in service use and reach the record table andpick-up arm, thereby interfering with the true sound reproduction fromthe record. The resultant spurious frequencies, or rumble as they arecalled in the art, are predominantly in the midbass to the sub-bassfrequency region and although they may not always be heard directly bythe human ear they tend to muddy the reproduction of the desired soundand, hence, impair the listeners enjoyment and increase listeningfatigue.

Various proposals have been made to correct this condition. One approachhas been to incorporate an electric rumble filter in the amplifyingsystem. While such filters do reduce the rumble they are objectionablein that they reduce the desired low frequency reproduction from therecord as well. Another suggestion has been to mount the pick-up armsomewhere other than on the mounting board but this solution has thedrawback of destroying the unitary structure of the turntable assembly avery important consideration as this assembly is widely .sold as aunitary component of a record playing system.

It is an object of my invention to provide a supporting structure forthe pick-up arm, or for the pick-up arm and the record table, that willisolate either the pick-up :arm or both the pick-up arm and the recordtable from these spurious frequencies which would otherwise impair thesound reproduction from the record. A further o ject of my invention isto provide such a supporting structure which may be incorporated in themounting board and sold therewith as a single unit. Still another objectof my invention is to provide such a supporting structure capable ofaccepting standard commercial pickup arms of various types and lengthswithout impairing the tracking ability of the arms. Another object of myinvention is to eliminate all mass in the record table in excess of thatrequired for stable rotational speed.

Briefly and generally, my invention comprises a turntable assembly inwhich the supporting structure for the pick-up arm, or for the recordtable and the pick-up arm, is inertially stabilized against frequenciesin the audio range. This is accomplished by so constructing :andmounting the supporting structure on the mounting board that the naturalfrequency of vibration of the supporting structure, including thepick-up arm, or the pick-up arm and record table, is in all directionswell below the audio frequency range. Preferably, this is accomplishedby suspending the-supporting structure from the mounting board throughsuitable means having compliance properly related to the mass of thesupporting structure and accessories.

In one preferred form of the invention shown and described herein, thesupporting structure comprises a platform for the pick-up arm mountedsubstantially in the plane of the mounting board and positioned withinan opening therein with clearance all around. Depending from thisplatform and rigidly secured thereto is a weighted member having a massmany times greater than that of the pick-up arm. This member, in turn,is resiliently connected to the mounting board by means of a pluralityof springs which support the weight of the supporting structure andwhich are positioned so as to maintain the supporting structure in adefinite position of rest. Additionally, a rigid safety bracket isprovided on the underside of the mounting board and passed underneaththe supporting structure in order to limit the motion of the structureif an abnormally large downward force should accidentally be applied. Asuitable pad is interposed between this rigid bracket and the weightedmember so as to act a sa damping means and protective cushion for theweighted member.

In another preferred form of the invention, shown and described herein,the supporting structure depending from the pick-up arm platform is madesubstantially larger and is extended so as to lie underneath the shaftfor the record table. The supporting structure comprises a framework,which may advantageously be made in the form of a cross and may, at itscenter, carry the bearing housing for the shaft of the record turntable.As in the embodiment previously described above, the platform for thepick-up arm is mounted substantially in the plane of the mounting boardand positioned within an opening therein with clearance all around.Similarly, the platform is rigidly connected to the framework and theframework is suspended from the mounting board by a plurality ofsprings. The bearing housing for the record turntable shaft extendsupwardly through an opening in the mounting board with clearance allaround, thus, the springs support both the record turntable and theplatform for the pick-up arm in suitable relationship with the mountingboard. By this construction the weight of the turntable serves not onlyto stabilize rotational speed but to inertially stabilize the platformfor the pick-up arm as well, thus obviating the need for any additionalweighted member. Means for adjusting the amount of spring force adjacentthe platform of the pick-up arm is provided so thatthe platform maybe'leveled for various weights and lengths of the pick-up arms which maybe utilized in the assembly.

It will be understood that the foregoing general descrip tion and thefollowing detailed description as'well are exemplary and explanatory ofthe invention but are not restrictive thereof.

Of the drawings: 4 V

FIG. 1 is a top plan view of a phonograph turntable assembly constructedin accordance with the teaching of the present invention;

FIG. 2 is a side elevational view, partly in section, taken along theline 2-2. in FIG. 1 looking in the direction of the arrows;

FIG. 3 is a sectional view taken along the line 33 of FIG. 1 looking inthe direction of the arrows;

FIG. 4 is a perspective view showing how the supporting structure ismounted within the opening in the mounting'board;

FIG. 5 is a top plan view of another phonograph turntable assemblyconstructed in accordance with the teachings of the present invention;

FIG. 6 is a bottom plan view of the embodiment shown in FIG. 5;

FIG. 7 is a sectional view taken along the line 7-7 in FIG. looking inthe direction of the arrows;

FIG. 8 is an enlarged sectional view taken along tire line 88 in FIG. 6looking in the direction of the arrows;

FIG. 9 is a sectional view taken along the line 9-3 in FIG. 6 looking inthe direction of the arrows.

A detailed description of the invention will now be given with referenceto the preferred embodiment of the invention shown in FIGS. 1-4. Thephonograph turntable assembly comprises a mounting board 10, having legs12, each of which is provided with a coiled spring 14 extendingtherebelow in order to provide a resileint mounting for the mountingboard within the cabinet or other enclosure (not shown) of thephonograph system. Mounted on the board is a rotatable turntable 16having a vertically arranged shaft which rotates in a bearing housing 18that extends through the mounting board It}. A driving motor 20 for theturntable 16 is generally mounted underneath the mounting board but thedrive shaft 21 therefor extends upwardly through the mounting board andis provided with three pulleys 22, 24, 26 thereon. The power of themotor shaft 21 is transferred to the turntable 16 by means of an endlessbelt 28 that passes around the turntable and a pulley on the motorshaft.

Adjacent one corner of the mounting board 10 there is provided agenerally rectangular opening 30 therein and it is within this openingthat the supporting structure 32 for the pick-up arm 34 is located. Asshown in the drawing, the supporting structure 32 for the pick-up armcomprises a platform 36 having a substantially rectangular configurationthat enables it to fit in the corresponding opening 30 in the mountingboard 10 yet with a definite clearance all around its periphery.Depending from the platform 36 and rigidly secured thereto by means ofthe posts 38 is a weighted member 40 whose mass is several times greaterthan the mass of the pick-up arm 34- and which is rectangular in shape.Four coiled springs 42 are connected to the weighted member 40 and tothe underside of the mounting board. These serve to support thesupporting structure 32 for the pick-up arm.

In order to keep the supporting structure centered in substantially thesame position, the springs 42 are located so that they are splayed to aslight degree, that is, the upper portions 44 of the springs 42 arepositioned outwardly of the lower portions 46 of the springs where theyare connected onto the weighted member 40. Additionally, a rigidU-shaped bracket member 48 is secured to the underside of the mountingboard 10 adjacent the opening 30 and passes underneath the weightedmember 40 at some distance therefrom. Interposed between the bracket 48and the weighted member 40 is a pad 50 made from suitable dampingmaterial which, together with the bracket, serves to limit the downwardmovement of the supporting structure and to serve as a damping meanstherefor.

The platform 36 for the pick-up arm is made large enough to accommodatepick-up arms of conventional commercial types and lengths as desired.

The weight of the member 40 and the compliance of the springs 42 areselected so that the natural frequency of the supporting structure inall directions is well below the lowest audible frequency, which isapproximately 20 cycles per second. In this way the supporting structure32 as a whole is inertially stabilized against any frequencies in theaudio range. Should any frequencies above the natural frequency of thesupporting structure reach the structure they will be effectivelyattenuated through the resistance of the mass of the weighted structure32 to vibration at those frequencies. In addition to having a weightgreat enough to lower the natural frequency of the structure 32 belowthe audio range it is also necessary that the total weight of structure32 be sufficiently greater than the weight of any pick-up arm mounted onthe platform 4 36 so that the added weight of the arm will notobjectionably tilt or lower the structure from its normal unloadedposition; otherwise the positioning of the arm on the platform forcorrect overhang or underhang would become difficult and the tracking ofthe arm could be impaired.

While the preferred embodiment of the invention described above showsthe platform 36 in the same plane as the mounting board 16, it is to beunderstood that the invention is not limited to such a coplanararrangement of these elements.

Referring now to FIGS. 59 there is shown another preerred embodiment ofthe applicants invention. In this form of the invention the phonographturntable assembly comprises a mounting board 11% removably resting on abox frame 111. As in the embodiment described above, the driving motor129 is generally mounted underneath the mounting board but the driveshaft 121 therefor extends upwardly through the mounting board and isprovided with one or more pulleys. The driving motor is suspended fromthe board on rubber shocks 123 or other resilient means to minimize thetransmission of sound from the motor which would be otherwise amplifiedby a rigid connection with the mounting board. An endless belt 128transmits power to the turntable 116. Similarly, an opening 130 isprovided in the mounting board and a platform 136, of slightly smallerdimensions than the opening 139, is positioned therein with clearanceall around. A pick-up arm 134 is mounted on the platform 136 but is of adifferent type and has a different length than the pick-up arm 34,accordingly, it is secured to the platform 136 at a different point. Theweighted member is formed by a framework 148 which extends beneath theplatform 136 for the pick-up arm 134 and the bearing housing 117 for theshaft of the record turntable 116. Preferably the framework 149 isformed in the shape of a cross although this particular configuration isnot necessary. As shown, framework 146 is formed by three channel barsor braces 150, 152, 154. Two of the braces 150, 152 are disposed alongthe same longitudinal axis and are joined one above the other by theposts 156 thus forming, in effect, a strong and rigid truss. The upperbrace 15!} extends at one end to a point underneath the central portionof the platform 136 and at its opposite end to a point underneath theperiphery of the record turntable 116. Interposed between the upper andlower braces 150, 152 is a cylindrical bushing 113 adapted to receivethe bearing housing 117 for the record turntable shaft extendingdownwardly through the opening 113 in the mounting board. Suitable nuts119 are provided to clamp the bushing 113 firmly with respect to thebraces 150, 152. The upper brace 150 is also rigidly secured to thecross brace 154. The bearing housing 117 is firmly locked in bushing 118by set screw 190 so as to provide the desired positioning of theframework with respect to the mounting board.

The framework is suspended from the mounting board 110 by means of foursprings 142 secured to the braces 150, 154 and recessed in openings inthe mounting board. At the end 158 a rigid removable connection 138 isprovided between the brace and the platform 136. Additionally, the brace150 is provided with an extension rod 160 bent at slight angle withrespect to the longitudinal axis of the brace and also downwardly withrespect to the plane of the brace. At its outer end 162 the rod 160 isflattened and attached by a spring 164 to an adjustable screw and nut166 secured on the mounting board 110, so as to provide adjustabletension on the framework at this point to compensate for variations inthe weights and dimensions of the various pick-up arms which may bemounted on the platform. In order to stabilize the platform horizontallythe brace 150 is provided with a spring-like finger 170 on which ismounted a felt pad 172 which bears very lightly against the undersurface of the mounting board 110. This arrangement provides a veryslight amount of damping between the framework 140 and the mountingboard 110 to stabilize the framework from displacements caused by anon-uniform or distorted belt, or from a slight imbalance in theturntable itself, or from the handling of the pick-up arm at the startof the record.

The compliances and dispositions of the supporting springs are chosen sothat, in combination with the weight of the turntable 116, the framework140, and the platform 136, natural frequencies of vibration in thevertical and the horizontal planes of approximately five cycles persecond or less are obtained. In conjunction with the slight damping ofthe felt pad 172 the arrangement provides almost perfect inertialstabilization of the pick-up arm and the record turntable. Consequently,vibrations in the mounting board do not muddy reproduction from therecord. By utilizing a suitably compliant endless belt 123 between themotor and the turntable the latter may be effectively isolated from anymotor vibrations which might otherwise be transmitted to the table fromthis source.

In order to facilitate transportation of the turntable assembly, meansare provided conveniently to secure the framework 140 and motor 120 tothe mounting board 110. A flange 180 strongly attached to the top of theturntable housing 117 may be tightened down firmly against the mountingboard 110 by four wood screws (not shown). Rigidly attached to the motor120 just below the mounting board are two metal brackets 182, each withtwo tapped holes 184 disposed to receive machine screws (not shown).These may conveniently be inserted and tightened so as to clamp themotor brackets firmly against the underside of the mounting board duringtransportation. Furthermore, dimensions can readily be chosen so that,while the housing 117 is clamped down for local transportation, theturntable weight will automatically be supported by suitable pads 186 onthe mounting board 110 and not by the more delicate end thrust bearing188 which bears the weight of the table in service use.

What is claimed is:

1. A phonograph turntable assembly including a mounting board withdriving motor secured thereon, a record turntable driven by said motorthrough resilient means and otherwise isolated from physical contactwith said motor, a bearing housing for said turntable, a platformadapted to receive a pick-up arm, second resilient means,

and a rigid supporting structure, said bearing housing and platformbeing attached in rigidly fixed relationship on said supportingstructure, said structure being coupled to said mounting board by saidsecond resilient means, and the combined mass of turntable, bearinghousing, structure and platform so proportioned to the resilient meansthat the combination can oscillate freely, in both vertical andhorizontal directions, only at frequencies below the audio range.

2. A phonograph turntable assembly as set forth in claim 1, includingadjustable means resiliently connected between said mounting board andsaid supporting structure and adapted to permit adjustable levelling ofsaid supporting structure to compensate for different loadings of saidplatform.

3. A phonograph turntable assembly as set forth in claim 1, includingauxiliary damping means connected between said supporting structure andsaid mounting board.

4. In a phonograph turntable assembly having a mounting frame withdriving motor attached thereto, a turntable with hearing means coupledresiliently to said motor and otherwise isolated from physical contactwith said motor, and a platform for mounting a-pick-up arm, means forrendering said turntable and platform jointly insensitive to spuriousvibrations in the mounting frame arising from motor unbalance and othersources, comprising a massive sub-chassis to which said turntablebearing and platform are secured in rigidly fixed relationship, saidsub-chassis being resiliently attached to the mounting frame so as topermit the sub-chassis, weighted by said turntable and platform, to havefree oscillation frequencies, vertical and horizontal, only in thesub-sonic range, whereby a record mounted on said turntable and saidpick-up are mounted on said platform are concurrently and inertiallystabilized.

5. A phonograph turntable assembly as set forth in claim 4 including anadjustable resilient coupling between said mounting frame andsub-chassis to permit levelling of the turntable and pick-up armplatform for different platform loads.

6. A phonograph turntable assembly as set forth in claim 4 includingmeans for exerting a slight damping,

between said mounting frame and sub-chassis, of vertical and horizontalrelative motions, so as to shorten the duration of any sub-sonicoscillation of the sub-chassis caused by shock and service use.

References Cited in the file of this patent UNITED STATES PATENTS1,555,150 Oswald Sept. 28, 1925 1,746,004 Marshall Feb. 4, 19301,917,633 Burt July 11, 1933 1,975,907 Strauss Oct. 9, 1934 2,891,409Hansen June 23, 1959 2,927,795 Drake Mar. 8, 1960 FOREIGN PATENTS112,116 Australia Dec. 19, 1940 740,896 Germany Oct. 11, 1944 575,069Great Britain Feb. 1, 1946 154,547 Australia Dec. 17, 1953 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.047.297 July 31,1962 Frederick H. Drake It is hereby certified that error appears in theabove numbered patent requiring correction and that the said LettersPatent should read as corrected below.

Column 6, line 25, for "are" read arm Signed and sealed this 27th day ofNovember 1962.

(SEAL) Attest: ESTON G. JOHNSON m swrm DAVID LAD) Attesting OfficerCommissioner of Patents

